Support of BBQ Dataset View

[lowener]

This PR introduce the structures used for the BBQ API. Related PR #2175
Those structures will be used for the support of compressed dataset in CAGRA and NN-Descent (#2326), as well as the BBQ Preprocessing Quantizer (#2162)

The quantizer views, dataset types and aliases are in the preprocessing/quantize/bbq.hpp to avoid circular dependencies

[achirkin]

This is a funny one :)

Suggested change

	template <typename T, typename IdxT, typename Accessor>
	using dense_owning_vector = std::conditional_t<Accessor::is_device_accessible,
	raft::device_vector<T, IdxT>,
	raft::host_vector<T, IdxT>>;
	template <typename T, typename IdxT, typename Accessor>
	using dense_view_vector = std::conditional_t<Accessor::is_device_accessible,
	raft::device_vector_view<T, IdxT>,
	raft::host_vector_view<T, IdxT>>;
	template <typename T, typename IdxT, typename Accessor>
	using vector = raft::mdarray<T, raft::vector_extent<IdxT>, raft::layout_c_contiguous, Accessor>
	template <typename T, typename IdxT, typename Accessor>
	using vector_view = raft::mdspan<T, raft::vector_extent<IdxT>, raft::layout_c_contiguous, Accessor>

1. Don't use host/device aliases as the base type - just use the accessor itself on the raw type
2. We have an established naming scheme for these: scalar/vector/matrix/mdarray and corresponding {object}_view
3. In the end, they really belong to raft rather than cuvs

You can have a look an mimic the definitions at https://github.com/NVIDIA/raft/blob/main/cpp/include/raft/core/device_mdarray.hpp and https://github.com/NVIDIA/raft/blob/main/cpp/include/raft/core/device_mdspan.hpp